Shop-API Error: Cannot Load Relation Type Custom Fields

[ban-am]

Describe the bug
When querying the activeOrder with custom relation fields on the OrderLine entity, the shop-api throws an error: Cannot read properties of undefined (reading 'filter'.
This issue occure only when eager: true.
This issue does not occur with the admin-api order(id: $id) query.
No stack trace in the server logs.

To Reproduce

1. Define custom ProductVariant fields for `OrderLine.

customFields: {
    OrderLine: [
      {
        name: 'material',
        type: 'relation',
        entity: ProductVariant,
        eager: true,
        nullable: true,
        public: true
      },
    ],
  }

2. Create order

# shop-api

mutation addItemToOrder($productVariantId: ID!, $quantity: Int!, $customFields: OrderLineCustomFieldsInput!) {
  addItemToOrder(productVariantId: $productVariantId, quantity: $quantity, customFields: $customFields) {
    __typename
  }
}

# Query Variables
{
  "productVariantId": "1", 
  "quantity": 1, 
  "customFields": {
    "materialId": "2"
  }
}

4. Query activeOrder using the shop-api with the custom fields.

query activeOrder {
  activeOrder {
    __typename
    lines {
      customFields {
        material {
          __typename
        }
      }
    }
  }

Expected behavior
The shop-api should load the relation type custom fields without any errors, similar to the admin-api.

Environment (please complete the following information):

• @vendure/core version: 2.1.9, 2.2.0-next.8 also tested
• Nodejs version: v18.20.1
• Database: postgres

Additional context
Repository https://github.com/ban-am/order-line-custom-relation-field-error

[ban-am]

While debugging the core package, I discovered that the method this.orderService.findOne(ctx, sessionOrder.id), invoked by activeOrder, successfully retrieves the custom field value. This same method is also called within the context of order(id: xxx) in the admin API. However, when the shop API makes a request, it results in an error, but the admin does not. Additionally, none of the middleware reported any errors. I’m uncertain about the next steps to take in troubleshooting this issue.